Producing an improved synthetic rubber from a multicomponent monomeric material



Patented June 24, 1952 .PRUDU'CING AN IMPROVED SYNTHETIC RUBBERFFROM' A MULTIGOMPGNEND MONOMERIC 'MATERIAL William B.- Reynolds, Bartlesville, Okla and Charles F.= Fryling', Phillips, .Tex,, ,assignors to .Phillips Petroleum-.'Company,..a corporation of Delaware 'No'l D'rawing. ApplicationiNovember Z5, 1949, Sel'ialvaNo. 129,516

the invention relates 1 to the production oil a .syn-

thetic rubber having-a high resistance-to failure inuse due .to physicaleauses.

Increasingainteresthas-been. shown in. elas .tomersr which are. adaptable .for lowv temperature applications-such as for useunder arcticconditionsv- QSy-nthetic rubber-.sucl ias -GRS.-is-not entirely satisfactory for such uses sinceit-becomes brittle at low temperatures and natural rubber also has drawbacks since it undergoes crystallization when exposed to lowtemperatures fcrlprolongedlperiods.

'We Ihave'. nowdiscover'e'd thatflpolyme'rs .of certain specific .multicomponent monomeric matei'ials have improved; propertiesand excellent processing characteristics. These polymers are produced by the polymerization of monomeric materials which are "mixturesof "-four, or more, polymerizable organic compounds, particularly mixtures of dienes. In someinstancea the monomeric material :can also contain vinyl a'ro matte compounds, such as ,1 styrene' a'nd "various substituted styrenes, and the like. Bheserpclym'ers from mul'ticomponent m'onomeric materials are particularly suitable for low temperatureapplic'a'tions since they not onlyhave low freezing po'ints but-are amorphousin nature and thereflforeadosnot have any tendency .to undergocrystallization. Inaddition xt'o= their properties whichmake them particularly adaptable for low temperature work; these .polymerssshow excellent tensile strength, elongation, hysteresis, andifl'ex lifeproperties;

"The object. of "this invention is to produce Ta syntheticriibberliaving good physicalproperties;

Another object" 'ofthis "invention iis td i'produce a synthetic rubber which'i's"suitableforuse at extremely low temperatures.

A further object of this inventionistoproduce a syntheticx-rubber having a good flex life and a lowahysteresis.

Eurther objects and advantages-of thisinvention will become apparent, to those skilled inzthe art; from. the accompanying disclosure-and-cdiscussion.

Ihe .pm'cess: of this invention, :and :the' synthetic rubber .polymer produced thereby, :is based upon our discovery that by polymerizing amonomericmaterlal comprising atlleast. four different conjugated .diolefinhydrocarbonsin approximately .=equal. proportions, the resulting-polymer has 'uniqueproperties. To. obtain best results the polymerization should be-conductedat as "lowxa polymerization temperature as. possible. preferably below. 0? .C. Our experience .in,po1ymeriz.- ing .a wide .variety .of monomeric materials, -from those composed .of asingle ingredient and'th'e conventional..butadiene-styrene mixture through complex v.monomeric. materials such as. discussed .hereinin.detail,..indicates that'thetemperature of polymerization more *impoitant',v as to the physical properties of the polymer, than the specific recipe employed. The "type "of catalyst activator system, and theitemperature; primarily influence "the. polymerizationfrate', whatever the composition. of the monomeric material used, while. physical'i properties of the polymer are infiuenced' by composition of the-monomeric material. and" byiipoly'mer'izat'ion temperature; "For ordinary" uses of synthetic rubber, more-favorable ipiiys'icarproperties result "from low polymerization temperatures; In connection "with the presentinvention, the "improved-"product "can result *from so-called' bulk, or 'homogeno'us-poly merization; using such a polymerization catalyst asflnely'divided*sodium or' potassium, and-can also-result from polymerization of the monomeric material'while dispersed in -an immiscible liquidi usually an aqueous medium, usingany-one of- "a "number of polymerization recipes; Si'nce 'faster -polymerization rates are usually obtained; at low"temp'eratures, with the latter type of process; this is -=tlieone whic'li will be primarily considered" in connection withthe present invention. One type of recipe which is usually'preferred 'i's as follows:

Parts byweight Monomeric" material; 1110 Aqueousphase 50 @0275 Emulsifying agent -1' to;- '5 Modifying-agent; 0;0'5 to: 2 Catalyst composition; 0 .1 to: 5

The catalyst compositiom; or catalyst-activator system}. can be any one which will -.:give asatis: factory -polymerizationrate.-=.a-tthe temperature chosen. Preferred:catalyst-compositions.include: a combination of an organic hydroperoxideand a reactant, such as (l-) a combination of a reducing sugar (or the like) and a salt of iron or similar heavy metal, (2) a ferrous pyrophosphate complex, alone or with such a reducing compound, (3) a polyamino compound (such as tetraethylenepentamine, and the like), etc.; or a diazothioether, either alone as discussed in Reynolds and Cotten application Serial No. 641,866, filed January 17, 1946, now Patent 2,501,692, issued March 28, 1950, or in combination with a ferricyanide and a mercaptan, as discussed by Kolthofi and Dale in Journal of Polymer Science, vol. 3, 400-409 (1948).

When using such a recipe, it is generally preferred that the emulsion be of an oil in water type, with the ratio of aqueous medium to monomeric material between about 0.511 and about 2.75:1, in parts by weight. It is frequently desirable to include water-soluble components in the aqueous phase, particularly when the polymerization temperatures are below freezing. In-

organic salts and alcohols can be so used. Al-

cohols which are applicable, when operating at low temperatures, comprise water-soluble compounds of both the monohydric and polyhydric types, and include methyl alcohol, ethylene glycol, glycerine, erythritol, and the like. The amount of alcoholic ingredient used in a polymerization recipe must be sufficient to prevent freezing of the aqueous phase and generally ranges from 20 to 80 parts per 100 parts of monomers charged. In most cases the amount of water employed is sufilcient to make the total quantity of the alcohol-water mixture equal 150 to 200 parts. In cases where it is desired to use a larger quantity of the alcohol-water mixture, say around 250 parts, the amount of alcohol may be increased to as much as 120 parts. It is preferred that the alcohol be such that it is substantially insoluble in the non-aqueous phase, and that 90 per cent or more, of the alcohol present be in the aqueous phase. A high-boiling alcohol such as glycerine is difiicult to recover from the resulting serum; a low-boilingv alcohol such as methanol is easily removed and'frequently preferred. Other aliphatic alcohols which are higher-boiling than methanol, such as propanol, however, are frequently less satisfactory. If the resulting latex tends to gel at low reaction temperatures, a larger proportion of aqueous phase should be used. In the practice of the invention suitable means will be necessary to establish and maintain an emulsion and to remove reaction heat to maintain a desired reaction temperature. The polymerization may be conducted in batches, semicontinuously, or contlnuously. The total pressure on the reactants is preferably at least as great as the total vapor pressure of the mixture, so that the initial reactants will be present in liquid phase. Usually 5 0 to 98 per cent of the monomeric material is polymerized.

The monomeric material employed in connection with the present invention is a mixture of approximately equal proportions by weight of at least four conjugated diolefin hydrocarbons selected from the group consisting of 1,3-butadiene, isoprene (2-methyl-l,3-butadiene), piperylene- (1,3-pentadiene), methylpentadiene (a term considered to be generic to the various methyl-1,3-pentadienes, and mixtures thereof), and dimethylbutadiene (2,3-dimethyl-1,3-butadiene). The reactive components of the monomeric material should comprise at least 90 per cent of such a mixture.

The tendency to crystallize or to become brittle when subjected to low temperatures makes many elastomers unsatisfactory for certain applications. The polymers of this invention, produced from at least four polymerizable materials, are amorphous in character and are therefore superior to natural rubber and synthetic elastomers such as conventional butadiene-styrene copolymers, for low temperature uses. While this inventionis not dependent upon any explanation of the structure of the polymers or the fact that they do not undergo crystallization, it is generally assumed that, in the polymerization of butadiene with other comonomers, the comonomer molecules attach themselves randomly to the growing polymer chain. This irregular arrangement in the structure of the polymer moleculewould tend to destroy crystallinity. Hence, the regions adjacent to the comonomer residues appear to be regions in which crystallinity would be inhibited. Other things being equal, the more comonomer residues per butadiene residue in the copolymer chain, the less the tendency for the copolymer to crystallize regardless of the nature of the comonomer molecules. The low freezing points of the multicomponent polymers is probably explained by the presence of the severalpolymerizable materials which serve as freezing point depressants on each other.

Advantages of this invention are illustrated by the following examples. The reactants, and their proportions, and the other specific ingredients of the recipes are presented as being typical and should not be construed to limit the invention unduly.

Example I A copolymer Was prepared at -1( C. accord ing to the following recipe, charging a monomeric material consisting of equal parts by weight of 1,3-butadiene, trans-1,3-pentadiene, isoprene, and 2-methyl-1,3-pentadiene.

1 A blend of tertiary C C14, and C1 aliphatic mercaptans 1n :1 ratio of 3 1 1 parts by weight.

The preparation of the activator was effected by heating a mixture of 2.2 parts by weight FeSO4.'7H2O and 5.0 parts Na4PzO1.l0Hz0 insufficient water to make volumes at 60 C. for 40 minutes. Polymerization was carried out in the usual manner. A conversion of 56 per cent was attained in 48 hours.

The polymer was compounded'according to the following recipe:

Parts by weight Elastomer 100 Furnace black 50 Zinc oxide 3 Asphalt softener 6 Sulfur 1.75 N-cyclohexyl-2-benzothiazolesulfenamide 0.8 Stearic acid 1 2 1 Omitted for control.

Goringeweseffected meteor F2ifor601minutes and hysical:properties detennineds= A 'lcontrel'rsam ples'was made by polymerizing a monomerio material" consisting of 72 parts=biitadiene and 28 parts styreneatafitl -ci; using a standard :potas sium' persulfaterecipe and: c ompounding there' sulting'*syntlietic rubber-iipolymer in the"foregoingrecipes Thea-followi-ng iresults\wereobtained:

g a l omv ponent Control Raw'Mboney MLr; 69 53, compounded Mooney, MS 31:" 32 stTeSSr$tIBiIl =properties atill)v F v 300%Modulus: l, 330 1, 890 Tensilmifl 2;:800. 2;,950 Elongation, Percent z 51 I 410 Stress=stranpropertis at 200F-l (45m'inute=- cure s Tensile 1, 1,60 Elongation, Per cent; 300' Unaged:

15. 8 Brittle point. 63 Oven-aged 24 hoursat-212 1 Hysteresis, AT, F.. 53. 2 Resilience, Ber cent. 70. 2 68. 8 Flex life at 210F., thou ends of flexures to failure 6.3 4.5

The extremelyrlow hysteresisrooupled Withthigh 3Q obtained...v The. tableialso presents thereompo- 6 were compounded; Triea olymerizaatiom recipes usediiin preparing thes' polymers ewasraas follows zt:

The-polymers; and natural rubben-were-eome pounded using the following reeipes iniipa tgsby weight.

When, these materials. were so. compounded,- and cured and tested in. the; standardQmanner, the resultsshownin the accompanyingtabl were;

sitions of the .variousmonomerici materials...

Sample No RubberTested Polymer Natural Conversion:

Hours Per Cent Properties of Rubber:

Mooney, ML4 Compounded Sample Unaged:

Mooney MS 1% Stress-Strain at 80 F.

Modulus Tensile Elongation, per cent Hysteresis AT, T. Flex life at 210 F (thousands of flexures to la ure) Oven Aged 24 hours at 212 F Raw Hysteresis, AT, F 57. 5 53. 2 61. 2 55. 1 68. 2 50. 5 Flex life at 210 F 7. 8 6. 3 4. 6 0. 1 0. 1 l2. 5

(thousands of flexures to failure) flex life, and also the very low compounded Mooney value show the superiority of the fourcomponent polymer over the control. This polymer had better dynamic properties than the control at -48 C. and did not exhibit the undesirable properties of natural rubber.

Example II A number of polymers were produced from several monomeric materials, at a polymerization temperature of --10 0., and resulting polymers It is to be noted that samples A and B have superior flex life, especially after aging, and low hysteresis, both of which are desired properties.

Example 111 A synthetic rubber was prepared from a monomeric material comprising a mixture of butadlene, isoprene, piperylene, methyl pentadiene, 2,3-dimethyl butadiene and styrene with the components being present in a 19/ 19/ 19/19/ 19/5 Weight ratio, except that 025 part mercaptan and a sample of smoked sheet (natural rubber) blend was used instead of 0.05 part. A conversion of 48.1 per cent was obtained in 23.5 hours. The polymer was compounded as in the preceding examples and cured at 307 F. as before. A sampic of this polymer was subjected to low temperatures together with samples of GR-S and natural rubber. The GR-S sample froze at -55 C. and the natural rubber at 65 C., while the multicomponent polymer remained amorphous under the same conditions.

As will be evident to those skilled in the art, various modifications of this invention can be made, or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

We claim:

1. A process for producing an improved syn thetic rubber, which comprises polymerizing an aqueous dispersion of a hydrocarbon monomeric material comprising at least 90 per cent by-weight of equal parts by weight of at least four members selected from the group consisting of buta diene, isoprene, piperylene, methylpentadiene, and dimethylbutadiene, at a polymerization temperature below C., and recovering a polymeric material so producced.

2. An improved synthetic rubber comprising a hydrocarbon copolymer of at least 90 per cent by weight of equal parts by weight of at least four members selected from the group consisting of 1,3-butadiene, isoprene, piperylene, methylpentadiene, and dimethylbutadiene, and which when compounded and vulcanized with carbon black and sulfur has a lower hysteresis, a greater flex life after aging, and a lower MS 1 Mooney viscosity than a synthetic rubber copolymer prepared under the same conditions from '70 parts Number Name Date 2,384,544 Fryling Sept. 11, 1945 2,384,574 Stewart et a1 Sept. 11, 1945 8 butadiene and 30 parts styrene, by weight, which has been similarly compounded and vulcanized.

3. A process for producing an improved synthetic rubber, which comprises polymerizing an aqueous dispersion of ahydrocarbon monomeric material consisting of equal parts by weight of butadiene, isoprene, piperylene, and methylpentadiene at a polymerization temperature below 0 C., and recovering a polymeric material so produced.

4. An improved synthetic rubber comprising a hydrocarbon copolymer of equal parts by weight of butadiene, isoprene, piperylene, and methylpentadiene, and which when compounded and vulcanized with carbon black and sulfur has a lower hysteresis, a greater flex life after aging, and a lower MS 1% Mooney viscosity than a synthetic rubber copolymer prepared under the same conditions from parts butadiene and 30 parts styrene, by weight, which has been similarly compounded and vulcanized.

The following references are of record in the file of this patent;

UNITED STATES PATENTS OTHER REFERENCES Shearon, Jr., et al.: Ind. and Eng. Chem., vol. 40, May 1948, pages 769-777. 

1. A PROCESS FOR PRODUCING AN IMPROVED SYNTHETIC RUBBER, WHICH COMPRISES POLYMERIZING AN AQUEOUS DISPERSION OF A HYDROCARBON MONOMERIC MATERIAL COMPRISING AT LEAST 90 PER CENT BY WEIGHT OF EQUAL PARTS BY WEIGHT OF AT LEAST FOUR MEMBERS SELECTED FROM THE GROUP CONSISTING OF BUTADIENE, ISOPRENE, PIPERYLENE, METHYLPENTADIENE, AND DIMETHYLBUTADIENE, AT A POLYMERIZATION TEMPERATURE BELOW 0* C., AND RECOVERING A POLYMERIC MATERIAL SO PRODUCCED. 